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Abstract:

The zirconium content of the alloy composition of a copper alloy wire is
3.0 to 7.0 atomic percent; and the copper alloy wire includes copper
matrix phases and composite phases composed of copper-zirconium compound
phases and copper phases. The copper matrix phases and the composite
phases form a matrix phase-composite phase fibrous structure and are
arranged alternately parallel to an axial direction as viewed in a
cross-section parallel to the axial direction and including a central
axis. The copper-zirconium compound phases and the copper phases in the
composite phases also form a composite phase inner fibrous structure and
are arranged alternately parallel to the axial direction at a phase pitch
of 50 nm or less as viewed in the above cross-section. This double
fibrous structure presumably makes the copper alloy wire densely fibrous
to provide a strengthening mechanism similar to the rule of mixture for
fiber-reinforced composite materials.

Claims:

1. A copper alloy wire comprising: copper matrix phases; and composite
phases comprising copper-zirconium compound phases and copper phases;
wherein the zirconium content of alloy composition is 3.0 to 7.0 atomic
percent; the copper matrix phases and the composite phases form a matrix
phase-composite phase fibrous structure and are arranged alternately
parallel to an axial direction as viewed in a cross-section parallel to
the axial direction and including a central axis; and the
copper-zirconium compound phases and the copper phases in the composite
phases form a composite phase inner fibrous structure and are arranged
alternately parallel to the axial direction at a phase pitch of 50 nm or
less as viewed in the cross-section.

2. The copper alloy wire according to claim 1, wherein the composite
phases contain 5% to 25% of amorphous phases in terms of area fraction as
viewed in the cross-section.

3. A copper alloy wire comprising: copper matrix phases; and composite
phases comprising copper-zirconium compound phases and copper phases;
wherein the zirconium content of alloy composition is 3.0 to 7.0 atomic
percent; the composite phases contain 5% to 25% of amorphous phases in
terms of area fraction as viewed in a cross-section parallel to an axial
direction and including a central axis.

4. The copper alloy wire according to claim 1, wherein the composite
phases occupy 40% to 60% of the copper alloy wire in terms of area
fraction as observed in a cross-section perpendicular to the axial
direction.

5. The copper alloy wire according to claim 1, wherein the
copper-zirconium compound phases in the composite phases have an average
width of 10 nm or less as viewed in a cross-section parallel to the axial
direction and including the central axis.

6. The copper alloy wire according to claim 1, wherein the copper matrix
phases comprise a plurality of copper phases forming a copper matrix
phase inner fibrous structure and having an average width of 100 nm or
less in a cross-section parallel to the axial direction and including the
central axis, and contain 0.1% to 5% of deformation twins present at an
angle of 20.degree. to 40.degree. with respect to the axial direction so
as not to straddle boundaries between the adjacent copper phases.

7. The copper alloy wire according to claim 1, wherein the
copper-zirconium compound phases are represented by the general formula
Cu9Zr2 and are amorphous phases in part or the entirety
thereof.

9. The copper alloy wire according to claim 1, wherein the
copper-zirconium compound phases contain oxygen and silicon and have a
mean atomic number Z of 20 to less than 29, the mean atomic number Z
being calculated from an elemental composition determined by quantitative
measurement of the O--K line, the Si--K line, the Cu--K line, and the
Zr-L line using the ZAF method based on EDX analysis; and the copper
matrix phases contain no oxygen.

10. The copper alloy wire according to claim 1, wherein the copper alloy
wire has an ultimate tensile strength in the axial direction of 1,300 MPa
or more and an electrical conductivity of 20% IACS or more.

11. The copper alloy wire according to claim 1, wherein the copper alloy
wire has an ultimate tensile strength in the axial direction of 2,200 MPa
or more, an electrical conductivity of 15% IACS or more.

12. A method for producing a copper alloy wire, comprising: (1) a melting
step of melting a raw material so as to prepare a copper alloy containing
3.0 to 7.0 atomic percent of zirconium; (2) a casting step of casting the
melt into an ingot having a secondary dendrite arm spacing (secondary
DAS) of 10.0 μm or less; and (3) a wire drawing step of cold-drawing
the ingot to a reduction of area of 99.00% or more.

13. The method for producing a copper alloy wire according to claim 12,
wherein the melt is cast into a bar-shaped ingot having a diameter of 3
to 10 mm using a copper mold in the casting step.

14. A method for producing a copper alloy wire, comprising: (1) a melting
step of melting a raw material so as to prepare a copper alloy containing
3.0 to 7.0 atomic percent of zirconium; (2) a casting step of casting the
melt into a bar-shaped ingot having a diameter of 3 to 10 mm using a
copper mold; and (3) a wire drawing step of cold-drawing the ingot to a
reduction of area of 99.00% or more.

15. The method for producing a copper alloy wire according to claim 12,
wherein shear wire drawing is performed in the wire drawing step.

16. The method for producing a copper alloy wire according to claim 12,
wherein the raw material contains 700 to 2,000 ppm by mass of oxygen in
the melting step.

17. The method for producing a copper alloy wire according claim 12,
wherein the raw material is melted using a vessel containing silicon or
aluminum in the melting step.

18. The method for producing a copper alloy wire according to claim 12,
wherein the raw material is melted while injecting an inert gas so as to
apply a pressure of 0.5 to 2.0 MPa to the raw material in the melting
step; and the melt is poured while injecting the inert gas so as to apply
a pressure of 0.5 to 2.0 MPa to the raw material in the casting step
continuously after the melting step.

19. The method for producing a copper alloy wire according to claim 17,
wherein the vessel has a tap hole in a bottom surface thereof.

20. The method for producing a copper alloy wire according to claim 12,
wherein the metal melted in the melting step is poured into a copper mold
or a carbon die in the casting step.

21. The method for producing a copper alloy wire according to claim 12,
wherein the melt is solidified in the casting step by quenching so that,
according to results of an analysis by the EDX-ZAF method, the amount of
zirconium contained in copper matrix phases in the ingot at room
temperature after the solidification is supersaturated at 0.3 atomic
percent or more.

22. The method for producing a copper alloy wire according to claim 12,
wherein the ingot is cold-drawn to a reduction of area of 99.00% or more
through one or more drawing passes in the wire drawing step, at least one
of the drawing passes having a reduction of area of 15% or more.

23. The method for producing a copper alloy wire according to claim 12,
wherein the wire drawing is performed in the wire drawing step after
cooling at least one of the material and equipment for wire drawing to a
temperature lower than room temperature.

Description:

[0002] Known copper alloys for wires include copper-zirconium alloys. For
example, PTL 1 proposes a copper alloy wire with improved electrical
conductivity and ultimate tensile strength produced by subjecting an
alloy containing 0.01% to 0.50% by weight of zirconium to solution
treatment, drawing the alloy to the final diameter, and subjecting the
wire to predetermined aging treatment. This copper alloy wire has
Cu3Zr precipitated in copper matrix phases to achieve a high
strength up to 730 MPa. In PTL 2, on the other hand, the present
inventors have proposed a copper alloy containing 0.05 to 8.0 atomic
percent of zirconium and having a two-phase structure in which copper
matrix phases and eutectic phases of copper and a copper-zirconium
compound are layered on top of each other and in which the adjacent
copper matrix phase crystal grains contact intermittently, thus achieving
a high strength up to 1,250 MPa.

CITATION LIST

Patent Literature

[0003] PTL 1: JP 2000-160311 A [0004] PTL 2: JP 2005-281757 A

DISCLOSURE OF INVENTION

[0005] However, the copper alloy wires disclosed in PTLs 1 and 2 may have
insufficient ultimate tensile strength, for example, if they are thinned,
and there is therefore a need for a higher strength.

[0006] A main object of the present invention, which has been made to
solve the above problem, is to provide a copper alloy wire with increased
ultimate tensile strength.

[0007] As a result of an intensive study for achieving the above object,
the present inventors have found that a copper alloy wire with high
strength can be achieved by casting a copper alloy containing 3.0 to 7.0
atomic percent of zirconium into a bar-shaped ingot having a diameter of
3 to 10 mm using a pure copper mold and drawing the ingot to a reduction
of area of 99.00% or more, thus completing the present invention.

[0008] The present invention provides a copper alloy wire comprising:
copper matrix phases; and composite phases comprising copper-zirconium
compound phases and copper phases; wherein the zirconium content of alloy
composition is 3.0 to 7.0 atomic percent; the copper matrix phases and
the composite phases form a matrix phase-composite phase fibrous
structure and are arranged alternately parallel to an axial direction as
viewed in a cross-section parallel to the axial direction and including a
central axis; and the copper-zirconium compound phases and the copper
phases in the composite phases form a composite phase inner fibrous
structure and are arranged alternately parallel to the axial direction at
a phase pitch of 50 nm or less as viewed in the cross-section.

[0009] The present invention also provides a copper alloy wire comprising:
copper matrix phases; and composite phases comprising copper-zirconium
compound phases and copper phases; wherein the zirconium content of alloy
composition is 3.0 to 7.0 atomic percent; and the composite phases
contain 5% to 25% of amorphous phases in terms of area fraction as viewed
in a cross-section parallel to an axial direction and including a central
axis.

[0010] The present invention further provides a method for producing a
copper alloy wire, comprising: (1) a melting step of melting a raw
material so as to prepare a copper alloy containing 3.0 to 7.0 atomic
percent of zirconium; (2) a casting step of casting the melt into an
ingot having a secondary dendrite arm spacing (secondary DAS) of 10.0
μm or less; and (3) a wire drawing step of cold-drawing the ingot to a
reduction of area of 99.00% or more.

[0011] The present invention still further provides a method for producing
a copper alloy wire, comprising: (1) a melting step of melting a raw
material so as to prepare a copper alloy containing 3.0 to 7.0 atomic
percent of zirconium; (2) a casting step of casting the melt into a
bar-shaped ingot having a diameter of 3 to 10 mm using a copper mold; and
(3) a wire drawing step of cold-drawing the ingot to a reduction of area
of 99.00% or more.

[0012] These copper alloy wires have increased ultimate tensile strength.
Although the reason for this effect remains uncertain, presumably the
double fibrous structure, namely, the matrix phase-composite phase
fibrous structure and the composite phase inner fibrous structure, makes
the copper alloy wire densely fibrous to provide a strengthening
mechanism similar to the rule of mixture for fiber-reinforced composite
materials. Alternatively, presumably the amorphous phases present in the
composite phases provide some strengthening mechanism.

BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1 is an illustration showing an example of a copper alloy wire
10 of the present invention.

[0014] FIG. 2 is an illustration showing an example of a cross-section of
the copper alloy wire 10 of the present invention parallel to the axial
direction and including the central axis.

[0015] FIG. 3 is an illustration showing an example of a cross-section of
the copper alloy wire 10 of the present invention parallel to the axial
direction and including the central axis.

[0025] FIG. 13 is a set of optical micrographs of the casting structures
of ingots containing 3.0 to 5.0 atomic percent of zirconium.

[0026]FIG. 14 is an SEM photograph of the casting structures of an ingots
containing 3.0 atomic percent of zirconium.

[0027] FIG. 15 is a set of SEM photographs of the cross-sections of the
copper alloy wire of Example 28.

[0028]FIG. 16 is a set of SEM photographs of the surface of the copper
alloy wire of Example 36.

[0029] FIG. 17 is a set of STEM photographs of a eutectic phase in the
copper alloy wire of Example 31.

[0030] FIG. 18 is a set of STEM photographs of a eutectic phase in the
copper alloy wire of Example 31.

[0031] FIG. 19 is a set of graphs showing the relationships between
eutectic phase fraction and EC, UTS, and σ0.2 of the examples
where drawing ratio η was 5.9.

[0032] FIG. 20 is a set of graphs showing the relationships between the
drawing ratio η and the EC, UTS, and σ0.2 of copper alloy
wires containing 4.0 atomic percent of zirconium.

[0033] FIG. 21 is a set of SEM photographs of longitudinal cross-sections
of the copper alloy wires containing 4.0 atomic percent of zirconium.

[0034] FIG. 22 is a graph showing the relationships between the annealing
temperature and the EC and UTS of annealed samples of the copper alloy
wire of Example 28.

[0035] FIG. 23 is a graph showing the nominal S-S curve of the copper
alloy wire of Example 36.

[0036] FIG. 24 is an SEM photograph of fracture surface of the copper
alloy wire of Example 36 after measurement of ultimate tensile strength.

[0037] FIG. 25 is a set of STEM photographs of a composite phase in a
longitudinal cross-section of the copper alloy wire of Example 33.

[0038] FIG. 26 shows the results of an EDX analysis of a eutectic phase in
the copper alloy wire of Example 33.

[0039] FIG. 27 shows the results of an EDX analysis of a copper matrix
phase in the copper alloy wire of Example 33.

[0040] FIG. 28 is a set of STEM-BF images of the copper alloy wire of
Example 33.

[0041] FIG. 29 is a set of graphs showing the relationships between the
eutectic phase fraction measured at a drawing ratio η of 5.9 and UTS,
σ0.2 Young's modulus, EC, elongation of copper alloy wires
where drawing ratio η was 8.6.

[0042] FIG. 30 is a set of graphs showing the relationships between the
drawing ratio and the UTS, σ0.2, structure, and EC of the
copper alloy wires containing 4 atomic percent of zirconium.

[0043] FIG. 31 summarizes the results of the examinations of the
relationships between the zirconium content and drawing ratio η and
the changes in layered structure and properties.

[0044] FIG. 32 is a graph showing the relationships between the UTS and EC
of the copper alloy wires of Examples 28 to 36 and Comparative Example 6.

BEST MODES FOR CARRYING OUT THE INVENTION

[0045] A copper alloy wire of the present invention will now be described
with reference to the drawings. FIG. 1 is an illustration showing an
example of a copper alloy wire 10 of the present invention, and FIGS. 2
and 3 are each an illustration showing an example of a cross-section of
the copper alloy wire 10 of the present invention parallel to the axial
direction and including the central axis. The copper alloy wire 10 of the
present invention includes copper matrix phases 30 and composite phases
20 composed of copper-zirconium compound phases 22 and copper phases 21.
In the copper alloy wire 10 of the present invention, the copper matrix
phases 30 and the composite phases 20 form a matrix phase-composite phase
fibrous structure and are arranged alternately parallel to the axial
direction as viewed in a cross-section parallel to the axial direction
and including the central axis.

[0046] The copper matrix phases 30 are formed of proeutectic copper and
form the matrix phase-composite phase fibrous structure together with the
composite phases 20. These copper matrix phases 30 increase the
electrical conductivity.

[0047] The composite phases 20 are composed of the copper-zirconium
compound phases 22 and the copper phases 21 and form the matrix
phase-composite phase fibrous structure together with the copper matrix
phases 30. In these composite phases 20, additionally, the
copper-zirconium compound phases 22 and the copper phases 21 form a
composite phase inner fibrous structure and are arranged alternately
parallel to the axial direction at a phase pitch of 50 nm or less as
viewed in a cross-section parallel to the axial direction and including
the central axis. The copper-zirconium compound phases 22 are formed of a
compound represented by the general formula Cu9Zr2. The phase
pitch may be 50 nm or less, preferably 40 nm or less, more preferably 30
nm or less. This is because a phase pitch of 50 nm or less further
increases the ultimate tensile strength. On the other hand, the phase
pitch is preferably larger than 7 nm, and in view of facilitating
production, more preferably 10 nm or more, further preferably 20 nm or
more. The phase pitch can be determined as follows. First, a wire thinned
by argon ion milling is prepared as a sample for STEM observation. Next,
a region where eutectic phases can be recognized in the central region,
serving as a representative region, is observed at a magnification of
500,000 times or more, for example, 500,000 or 2,500,000 times, and
scanning electron microscopy high-angle annular dark-field images
(STEM-HAADF images) are acquired, for example, in three fields of view of
300 nm×300 nm for a magnification of 500,000 times or in ten fields
of view of 50 nm×50 nm for a magnification of 2,500,000 times.
Then, the widths of all copper-zirconium compound phases 22 and copper
phases 21 whose widths can be examined in the STEM-HAADF images are
measured, are added together, and are divided by the total number of
copper-zirconium compound phases 22 and copper phases 21 whose widths
were measured to calculate the average thereof as the phase pitch.
Preferably, the copper-zirconium compound phases 22 and the copper phases
21 are arranged alternately at a substantially regular pitch in view of
increasing the ultimate tensile strength.

[0048] The composite phases 20 preferably contain 5% to 35%, more
preferably 5% to 25%, of amorphous phases in terms of area fraction as
viewed in a cross-section parallel to the axial direction and including
the central axis. That is, the area fraction of the amorphous phases in
the composite phases 20 is preferably 5% to 35%, more preferably 5% to
25%. In particular, the area fraction is more preferably 10% or more,
further preferably 15% or more. This is because an area fraction of the
amorphous phases of 5% or more further increases the ultimate tensile
strength. On the other hand, a copper alloy wire containing 35% or more
of amorphous phases is difficult to produce. As shown in FIG. 3,
amorphous phases 25 are mainly formed at the interfaces between the
copper-zirconium compound phases 22 and the copper phases 21, presumably
contributing to maintaining sufficient ultimate tensile strength. The
area fraction of the amorphous phases can be determined as follows.
First, a wire thinned by argon ion milling is prepared as a sample for
STEM observation. Next, a region where eutectic phases can be recognized
in the central region, serving as a representative region, is observed at
a magnification of 500,000 times or more, for example, 500,000 or
2,500,000 times, and lattice images are acquired, for example, in three
fields of view of 300 nm×300 nm for a magnification of 500,000
times or in ten fields of view of 50 nm×50 nm for a magnification
of 2,500,000 times. Then, the area fractions of possible amorphous
regions where atoms are randomly arranged in the acquired STEM lattice
images are measured, and the average thereof is calculated as the area
fraction of the amorphous phases (hereinafter also referred to as
"amorphous fraction").

[0049] The composite phases preferably occupy 40% to 60%, more preferably
45% to 60%, and further preferably 50% to 60%, of the copper alloy wire
10 of the present invention in terms of area fraction as observed in a
cross-section perpendicular to the axial direction. This is because an
area fraction of 40% or more further increases the strength, whereas an
area fraction of 60% or less, at which the amount of composite phases is
not excessive, prevents a possible break originating from the hard
copper-zirconium compound during wire drawing. The area fraction of the
composite phases presumably does not exceed 60% within the composition
range of the present invention. In addition, if the copper alloy wire is
used as a conductive wire, the area fraction of the composite phases 20
is preferably 40% to 50%. This is because an area fraction of the
composite phases of 40% to 50% further increases the electrical
conductivity, where presumably the copper matrix phases 30 serve as a
free electron conductor to maintain sufficient electrical conductivity,
whereas the composite phases 20, containing the copper-zirconium
compound, maintain sufficient mechanical strength. As used herein, the
term "electrical conductivity" refers to the electrical conductivity
represented as a proportion relative to the electrical conductivity of
annealed pure copper, which is defined as 100%, and is expressed in %
IACS (the same applied hereinafter). The area fraction of the composite
phases 20 can be determined as follows. First, a drawn copper alloy wire
is observed by SEM in a circular cross-section perpendicular to the axial
direction. Next, the black-and-white contrast of composite phases (white
regions) and copper matrix phases (black regions) is binarized to
determine the fraction of the composite phases in the entire
cross-section. The resultant value is used as the area fraction of the
composite phases (hereinafter also referred to as "composite phase
fraction").

[0050] The zirconium content of the alloy composition of the copper alloy
wire 10 of the present invention is 3.0 to 7.0 atomic percent. Although
the balance may include elements other than copper, the balance is
preferably copper and incidental impurities, and the amount of incidental
impurities is preferably as small as possible. Specifically, the copper
alloy is preferably a copper-zirconium binary alloy represented by the
composition formula Cu100-xZrx, wherein x is 3.0 to 7.0. The
zirconium content may be 3.0 to 7.0 atomic percent, preferably 4.0 to 6.8
atomic percent, more preferably 5.0 to 6.8 atomic percent. FIG. 4 is an
equilibrium diagram of copper-zirconium binary alloy. According to this
diagram, presumably the composition of the copper alloy wire of the
present invention is a hypoeutectic composition of copper and
Cu9Zr2, and the composite phases 20 are eutectic phases of
copper and Cu9Zr2. A zirconium content of 3.0 atomic percent or
more further increases the ultimate tensile strength because the amount
of eutectic phases is not too small. On the other hand, a zirconium
content of 7.0 atomic percent or less prevents, for example, a possible
break originating from hard Cu9Zr2 during wire drawing because
the amount of eutectic phases is not too large. In particular, a binary
alloy composition represented by the composition formula
Cu100-xZrx is preferred in that an appropriate amount of
eutectic phases can be more easily formed. In addition, a binary alloy
composition is preferred in that it facilitates management for reuse of
scrap materials, other than products, produced during manufacture and
scrap parts scrapped after their useful lives, as remelted materials.

[0051] The copper alloy wire 10 of the present invention has an ultimate
tensile strength in the axial direction of 1,300 MPa or more and an
electrical conductivity of 20% IACS or more. In addition, the ultimate
tensile strength can be increased to 1,500 MPa or more, or to 1,700 MPa
or more, depending on the alloy composition and the structure control.
For example, a higher ultimate tensile strength can be achieved by
increasing the zirconium content (atomic percent), increasing the
eutectic phase fraction, reducing the phase pitch, or increasing the
amorphous fraction. The reason for such a high ultimate tensile strength
is presumably that the double fibrous structure, namely, the matrix
phase-composite phase fibrous structure and the composite phase inner
fibrous structure, makes the copper alloy wire 10 densely fibrous to
provide a strengthening mechanism similar to the rule of mixture for
fiber-reinforced composite materials.

[0052] The copper alloy wire 10 of the present invention preferably has a
diameter of 0.100 mm or less. In particular, the diameter is more
preferably 0.040 mm or less, further preferably 0.010 mm or less. The
present invention is highly significant to apply to such extremely thin
wires because they often result in low production yield due to, for
example, a break during wire drawing or stranding because of their
insufficient ultimate tensile strength as elemental wires. On the other
hand, the diameter is preferably larger than 0.003 mm, and in view of
facilitating working, more preferably 0.005 mm or more, further
preferably 0.008 mm or more.

[0053] The copper alloy wire 10 of the present. invention has the
following applications. For example, the copper alloy wire 10 increases
the density of stator windings of a stepping motor, thus enabling the
development of a high-performance motor component that produces high
torque despite its compactness. In addition, the copper alloy wire 10
reduces the diameters of outer shield wires and central conductor
stranded wires of a coaxial cable. to increase the number of inner cores
while reducing the outer diameter of the cable. This contributes to a
higher performance in electronic devices and medical devices. The copper
alloy wire 10 can also be applied to a high-performance flexible flat
cable (FFC) that is thinner and more resistant to break. When used as an
electrode wire for wire electrical discharge machining, the copper alloy
wire 10 minimizes the machining allowance, thus enabling machining with
high dimensional accuracy. Furthermore, when used as an antenna wire or a
radio-frequency shield wire installed in a portable electronic device,
the copper alloy wire 10 reduces constraints on the installation site to
broaden the flexibility of radio-frequency circuit design, and even
reduces constraints on the shapes and installation sites of parts. In
another application, the copper alloy wire 10 provides an ultrathin coil
for potential use in a non-contact charging module in a compact
electronic device and also improves the charging performance thereof
because it increases the winding density per unit volume.

[0054] Next, a method for producing the copper alloy wire 10 will be
described. The method for producing the copper alloy wire of the present
invention may include (1) a melting step of melting a raw material, (2) a
casting step of casting the melt into an ingot, and (3) a wire drawing
step of cold-drawing the ingot. The individual steps will now be
sequentially described.

[0055] FIG. 5 is an illustration schematically showing a copper alloy in
the individual steps of the method for producing the copper alloy wire of
the present invention. FIG. 5(a) is an illustration showing a melt 50
melted in the melting step, FIG. 5(b) is an illustration showing an ingot
60 formed in the casting step, and FIG. 5(c) is an illustration showing
the copper alloy wire 10 formed in the wire drawing step.

[0056] (1) Melting Step

[0057] In the melting step, as shown in FIG. 5(a), a process for preparing
the melt 50 by melting the raw material is carried out. The raw material
used may be any material from which a copper alloy containing 3.0 to 7.0
atomic percent of zirconium can be prepared and may be either an alloy or
a pure metal. A copper alloy containing 3.0 to 7.0 atomic percent of
zirconium is suitable for cold working. In addition, this copper alloy is
preferred in that it has good melt flow because it has low melt viscosity
due to its alloy composition close to the eutectic composition.
Preferably, the raw material contains no element other than copper and
zirconium. In this case, an appropriate amount of eutectic phases can be
more readily formed. The melting process may be, for example, but not
limited to, a common process such as high-frequency induction melting,
low-frequency induction melting, arc melting, or electron beam melting,
or may be levitation melting. Of these, high-frequency induction melting
and levitation melting are preferably used. High-frequency induction
melting is preferred in that it allows melting in high volume at one
time, whereas levitation melting, in which molten metal is levitated
during melting, is preferred in that it more effectively inhibits molten
metal from being contaminated with impurities from, for example,
crucibles. The melting atmosphere is preferably a vacuum atmosphere or an
inert atmosphere. The inert atmosphere may be any gas atmosphere that
does not affect the alloy composition, for example, a nitrogen
atmosphere, a helium atmosphere, or an argon atmosphere. Of these, an
argon atmosphere is preferably used.

[0058] (2) Casting Step

[0059] In this step, a process for casting the melt 50 by pouring it into
a mold is carried out. As shown in FIG. 5(b), the ingot 60 has a
dendritic structure including a plurality of dendrites 65. The dendrites
65 are formed only of proeutectic copper phases and each include a
primary dendrite arm 66 serving as a trunk and a plurality of secondary
dendrite arms 67 serving as branches extending from the primary dendrite
arm 66. The secondary dendrite arms 67 extend from the primary dendrite
arm 66 substantially perpendicularly.

[0060] In this step, the melt 50 is cast into an ingot having a secondary
dendrite arm spacing (secondary DAS) of 10.0 μm or less. The secondary
DAS may be 10.0 μm or less, preferably 9.4 μm or less, more
preferably 4.1 μm or less. If the secondary DAS is 10.0 μm or less,
the copper matrix phases 30 and the composite phases 20 form a dense
fibrous structure extending in one direction in the subsequent wire
drawing step, thus further increasing the ultimate tensile strength. On
the other hand, the secondary DAS is preferably larger than 1.0 μm,
more preferably 1.6 μm or more, in view of ingot casting. The
secondary DAS can be determined as follows. First, three dendrites 65
having a series of four or more secondary dendrite arms 67 are selected
in a cross-section of the ingot 60 perpendicular to the axial direction.
Next, each spacing 68 between the series of four secondary dendrite arms
67 of each dendrite 65 is measured. Then, the average of a total of nine
spacings 68 is calculated as the secondary DAS.

[0061] The casting process may be, for example, but not limited to,
permanent mold casting or low-pressure casting, or may be a die casting
process such as normal die casting, squeeze casting, or vacuum die
casting. Continuous casting can also be employed. The mold used for
casting is preferably one having high thermal conductivity, for example,
a copper mold. The use of a copper mold, which has high thermal
conductivity, accelerates the cooling rate during casting, thus further
reducing the secondary DAS. The copper mold used is preferably a pure
copper mold, although it may be any copper mold having a thermal
conductivity similar to that of a pure copper mold (for example, about
350 to 450 W/(mK) at 25° C.). Although the structure of the mold
is not particularly limited, a water-cooled pipe may be installed inside
the mold to adjust the cooling rate. The shape of the resultant ingot 60
is preferably, but not limited to, an elongated bar shape. This
accelerates the cooling rate. In particular, a round bar shape is
preferred. This is because a more uniform casting structure can be
achieved. Whereas the casting process for forming the ingot 60 has been
described above, it is particularly suitable to form a bar-shaped ingot
having a diameter of 3 to 10 mm by casting using a copper mold. This is
because a diameter of 3 mm or more allows a better melt flow, whereas a
diameter of 10 mm or less further reduces the secondary DAS. The pouring
temperature is preferably 1,100° C. to 1,300° C., more
preferably 1,150° C. to 1,250° C. This is because a pouring
temperature of 1,100° C. or more allows a good melt flow, whereas
a pouring temperature of 1,300° C. or less causes little
deterioration of the mold.

[0062] (3) Wire Drawing Step

[0063] In this step, a process for forming the copper alloy wire 10 shown
in FIGS. 5(c) and 1 by drawing the ingot 60 is carried out. In this step,
the ingot 60 is cold-drawn to a reduction of area of 99.00% or more. As
used herein, the term "cold" refers to working at room temperature
without heating. Thus, cold wire drawing presumably inhibits
recrystallization, thus making it possible to easily provide a copper
alloy wire 10 densely fibrous with the double fibrous structure, namely,
the matrix phase-composite phase fibrous structure and the composite
phase inner fibrous structure. In addition, cold wire drawing simplifies
the production process for increased productivity because the copper
alloy wire 10 can be produced only by cold wire drawing without the need
for annealing during the working of the ingot 60 into the copper alloy
wire 10 or aging after the working. The wire drawing process may be, for
example, but not limited to, hole die drawing or roller die drawing, more
preferably a wire drawing process by which a shear force is applied in a
direction parallel to the axis so that the material undergoes shear slip
deformation. Such wire drawing is also herein referred to as "shear wire
drawing." The shear slip deformation, as caused by shear wire drawing,
presumably makes the fibrous structure more uniform, thus further
increasing the ultimate tensile strength. The shear slip deformation may
be, for example, simple shear deformation applied by drawing the material
through a die while causing friction at the surface in contact with the
die. The wire drawing step may be carried out by drawing the ingot 60 to
a reduction of area of 99.00% or more through a plurality of dies of
different sizes. In this case, a break is less likely to occur during the
wire drawing. The hole of the drawing die does not have to be circular;
instead, a die for square wires, a die for wires of special shape, or a
die for tubes may be used. The reduction of area may be 99.00% or more,
preferably 99.50% or more, more preferably 99.80% or more. This is
because a higher reduction of area further increases the ultimate tensile
strength. Although the reason for this remains uncertain, the ultimate
tensile strength increases with increasing drawing ratio presumably
because the crystal structure is distorted as the composite phases 20
change their crystal structure to occupy a larger area as viewed in
cross-section, or as the copper matrix phases 30 deform preferentially to
occupy a smaller area as viewed in cross-section. Another possible cause
is that copper and Cu9Zr2, which are thought to form an fcc
structure and a superlattice, respectively, become partially amorphous
after heavy working. The present inventors have carried out wire drawing
of ingots produced under the same conditions at varying reductions of
area (drawing ratios) and have demonstrated that the volume of the
composite phases 20 increases with increasing reduction rate. The
reduction of area may be less than 100.00% and is preferably 99.9999% or
less in view of working. The reduction of area can be determined as
follows. First, the cross-sectional area of the ingot 60 before the wire
drawing in a cross-section perpendicular to the axial direction is
determined. After the wire drawing, the cross-sectional area of the
copper alloy wire 10 in a cross-section perpendicular to the axial
direction is determined. The reduction of area (%) is then determined by
calculating {(cross-sectional area before wire drawing-cross-sectional
area after wire drawing)×100}/(cross-sectional area before wire
drawing). The drawing speed is preferably, but not limited to, 10 to 200
m/min, more preferably 20 to 100 m/min. This is because a drawing speed
of 10 m/min or more allows efficient wire drawing, whereas a drawing
speed of 200 m/min or less more reliably prevents, for example, a break
during the wire drawing.

[0064] In the wire drawing step, the ingot 60 is preferably drawn to a
diameter of 0.100 mm or less, more preferably 0.040 mm or less, and
further preferably 0.010 mm or less. The present invention is highly
significant to apply to such extremely thin wires because they often
result in low production yield due to, for example, a break during wire
drawing or stranding because of their insufficient ultimate tensile
strength as elemental wires. On the other hand, the diameter is
preferably larger than 0.003 mm, and in view of facilitating working,
more preferably 0.005 mm or more, further preferably 0.008 mm or more.

[0065] In this wire drawing step, the copper alloy wire 10 is formed. This
copper alloy wire 10 includes the composite phases 20 composed of the
copper-zirconium compound phases 22 and the copper phases 21 and the
copper matrix phases 30. As shown in FIG. 2, the copper matrix phases 30
and the composite phases 20 form a matrix phase-composite phase fibrous
structure and are arranged alternately parallel to the axial direction as
viewed in a cross-section parallel to the axial direction and including
the central axis. In the composite phases 20, additionally, the
copper-zirconium compound phases 22 and the copper phases 21 form a
composite phase inner fibrous structure and are arranged alternately
parallel to the axial direction at a phase pitch of 50 nm or less as
viewed in a cross-section parallel to the axial direction and including
the central axis. Thus, presumably the double fibrous structure, namely,
the matrix phase-composite phase fibrous structure and the composite
phase inner fibrous structure, makes the copper alloy wire 10 densely
fibrous to provide a strengthening mechanism similar to the rule of
mixture for fiber-reinforced composite materials.

[0066] The present invention is not limited to the embodiment described
above; it can be practiced in various manners within the technical scope
thereof.

[0067] For example, in the embodiment described above, the copper alloy
wire 10 has the matrix phase-composite phase fibrous structure and the
composite phase inner fibrous structure and, in the composite phase inner
fibrous structure, the copper-zirconium compound phases and the copper
phases are arranged alternately parallel to the axial direction at a
phase pitch of 50 nm or less as viewed in a cross-section parallel to the
axial direction and including the central axis; instead, the copper alloy
wire 10 may include copper matrix phases and composite phases composed of
copper-zirconium compound phases and copper phases, the zirconium content
of the alloy composition may be 3.0 to 7.0 atomic percent, and the
composite phases may contain 5% to 25% of amorphous phases in terms of
area fraction as viewed in a cross-section parallel to the axial
direction and including the central axis. This is because an area
fraction of amorphous phases of 5% to 25% provides high ultimate tensile
strength. More preferably, in the above composite phases, the
copper-zirconium compound phases and the copper phases form a composite
phase inner fibrous structure and are arranged alternately parallel to
the axial direction as viewed in a cross-section parallel to the axial
direction and including the central axis. This further increases the
ultimate tensile strength.

[0068] Whereas the method for producing the copper alloy wire 10 according
to the embodiment described above includes the casting step of casting
the melt 50 into an ingot having a secondary DAS of 10.0 μm or less,
it may instead include a casting step of casting the melt 50 into a
bar-shaped ingot having a diameter of 3 to 10 mm using a copper mold.
This provides a copper alloy wire 10 having high ultimate tensile
strength.

[0069] Whereas the method for producing the copper alloy wire 10 according
to the embodiment described above includes the melting step, the casting
step, and the wire drawing step, it may include other steps. For example,
a holding step, that is, a step of holding the melt, may be included
between the melting step and the casting step. If the holding step is
included, melting can be started in the melting furnace immediately after
transferring the melt to a holding furnace without waiting for all the
melt melted in the melting step to be completely cast, thus further
increasing the utilization of the melting furnace. In addition, if
component adjustment is performed in the holding step, finer adjustment
can be more readily performed. In addition, a cooling step of cooling the
ingot may be included between the casting step and the wire drawing step.
This reduces the time from casting to wire drawing.

[0070] Whereas the melting, casting, and wire drawing steps of the method
for producing the copper alloy wire 10 according to the embodiment
described above are described as separate steps, the individual steps may
be continuous without clear boundaries therebetween, as in continuous
casting and wire drawing, which is employed as an integrated process of
producing, for example, copper wires. This allows more efficient
production of the copper alloy wire 10.

[0071] The above description of the copper alloy wire and the method for
producing the copper alloy wire of the present invention is directed to
alloy compositions containing 3.0 to 7.0 atomic percent of zirconium,
with the balance being copper, and containing as small amounts of other
elements as possible (hereinafter also referred to as "other-element-free
materials"). As a result of a further study, the present inventors have
found that alloy compositions containing components other than copper and
zirconium (hereinafter also referred to as "other-element-containing
materials") provide higher strength. Preferred embodiments of
other-element-containing materials will now be described. Because the
basic composition and method for production are common to
other-element-free materials and other-element-containing materials, the
above description of other-element-free materials applies to
other-element-containing materials for common details; therefore, a
description thereof will be omitted.

[0072] In the copper alloy wire of the present invention, the copper
matrix phases may be further divided into a plurality of copper phases in
fibrous form (hereinafter also referred to as "layered" because they are
layered as observed in a cross-section). That is, the copper matrix
phases 30 may be composed of a plurality of copper phases forming a
copper matrix phase inner fibrous structure and arranged alternately
parallel to the axial direction as viewed in a cross-section parallel to
the axial direction and including the central axis. In this case, the
average width of the plurality of copper phases is preferably 150 nm or
less, more preferably 100 nm or less, and further preferably 50 nm or
less. Thus, if a copper matrix phase inner fibrous structure is formed in
the copper matrix phases 30, presumably the ultimate tensile strength can
be further increased by the effect similar to the Hall-Petch law, which
states that the ultimate tensile strength increases as the grain size
becomes smaller. At the same time, the copper matrix phases preferably
contain deformation twins. Thus, if the copper matrix phases contain
deformation twins, presumably the ultimate tensile strength can be
increased as a result of twinning without significantly decreasing the
electrical conductivity. The deformation twins are preferably present at
an angle of 20° to 40° with reference to the axial
direction so as not to straddle the boundaries between the adjacent
copper phases as viewed in a cross-section parallel to the axial
direction and including the central axis. In addition, the copper matrix
phases preferably contain 0.1% to 5% of deformation twins. In addition,
it is preferable that almost no dislocations be found in the
α-copper phases and the copper-zirconium compound phases, at least
in a longitudinal cross-section. In particular, presumably the electrical
conductivity can be further increased if the α-copper phases, which
are good conductors, have fewer dislocations. For other-element-free
materials, the copper matrix phases may be divided into a plurality of
copper phases, may contain deformation twins, and may have fewer
dislocations. In such cases, presumably the ultimate tensile strength or
the electrical conductivity can be further increased.

[0073] In the copper alloy wire of the present invention, the average
width of the copper-zirconium compound phases as viewed in a
cross-section parallel to the axial direction and including the central
axis is preferably 20 nm or less, more preferably 10 nm or less, further
preferably 9 nm or less, and most preferably 7 nm or less. If the average
width is 20 nm or less, presumably the ultimate tensile strength can be
further increased. In addition, the copper-zirconium compound phases are
preferably represented by the general formula Cu9Zr2 and are
more preferably amorphous phases in part or the entirety thereof. This is
because presumably amorphous phases are readily formed in the
Cu9Zr2 phases. For other-element-free materials, presumably the
ultimate tensile strength can be further increased if the average width
of the copper-zirconium compound phases is 20 nm or less. For
other-element-free materials, additionally, the Cu9Zr2 phases
may be amorphous phases in part or the entirety thereof.

[0074] The copper alloy wire of the present invention may contain elements
other than copper and zirconium. For example, the copper alloy wire may
contain elements such as oxygen, silicon, and aluminum. In particular,
the copper alloy wire preferably contains oxygen because it makes the
copper alloy, particularly the Cu9Zr2 phases, more amorphous
for the unknown reason. In particular, the copper alloy becomes more
amorphous with increasing drawing ratio. The amount of oxygen in the raw
material composition is preferably, but not limited to, 700 to 2,000 ppm
by mass. In addition, oxygen is preferably contained in the copper alloy
wire, particularly, in the copper-zirconium compound phases. Similarly,
if silicon and aluminum are contained, they are preferably contained in
the copper-zirconium compound. In this case, the mean atomic number Z of
the copper-zirconium compound phases calculated from the elemental
composition determined by quantitative measurement of the O--K line, the
Si--K line, the Cu--K line, and the Zr-L line using the ZAF method based
on EDX analysis is preferably 20 to less than 29. More preferably, the
mean atomic number ZA of the copper-zirconium compound phases
calculated from the elemental composition determined by quantitative
measurement of the O--K line, the Si--K line, the Al--K line, the Cu--K
line, and the Zr-L line using the ZAF method based on EDX analysis is 20
to less than 29. If the mean atomic number Z is 20 or more, presumably
the amounts of oxygen and silicon are not excessive, so that the ultimate
tensile strength and the electrical conductivity can be further
increased. On the other hand, if the mean atomic number Z is less than
29, that is, less than the atomic number of copper, presumably the
proportion of oxygen and silicon and the proportion of copper and
zirconium are well-balanced, so that the ultimate tensile strength and
the electrical conductivity can be increased. In addition, the proportion
of zirconium in the copper alloy wire is preferably 3.0 to 6.0 atomic
percent. At the same time, the copper matrix phases preferably contain no
oxygen. As used herein, the phrase "contain no oxygen" refers to, for
example, containing an amount of oxygen that is undetectable in the above
quantitative measurement using the ZAF method based on EDX analysis. The
mean atomic number Z can be determined as the sum of the atomic number of
oxygen, 8, the atomic number of silicon, 14, the atomic number of copper,
29, and the atomic number of zirconium, 40, multiplied by the respective
elemental concentrations (in atomic percent) and divided by 100.

[0075] The copper alloy wire of the present invention has an ultimate
tensile strength in the axial direction of 1,300 MPa or more and an
electrical conductivity of 15% IACS or more. Furthermore, the ultimate
tensile strength can be increased to, for example, 1,500 MPa or more,
1,700 MPa or more, or 2,200 MPa or more, depending on the alloy
composition and the structure control. In addition, the electrical
conductivity in the axial direction can be increased to, for example, 16%
IACS or more, or 20% IACS or more, depending on the alloy composition and
the structure control. In addition, the Young's modulus in the axial
direction can be varied depending on the alloy composition and the
structure control. For example, the Young's modulus in the axial
direction can be characteristically decreased to 60 to 90 GPa, which is
nearly half those of typical copper alloys as disclosed in PTLs 1 and 2.
For other-element-free materials, presumably the Young's modulus can be
decreased to, for example, 110 to 140 GPa by controlling, for example,
the proportion of the amorphous phases.

[0076] Next, the production method will be described. In the method for
producing the copper alloy wire of the present invention, the raw
material used in the melting step may be a material containing at least
oxygen in addition to copper and zirconium. The amount of oxygen is
preferably 700 to 2,000 ppm by mass, more preferably 800 to 1,500 ppm by
mass. A material containing oxygen is preferred because it makes the
copper alloy, particularly the Cu9Zr2 phases, more amorphous
for the unknown reason. The vessel used for melting the raw material is
preferably a crucible. In addition, the vessel used for melting the raw
material is preferably, but not limited to, a vessel containing silicon
or aluminum, more preferably a vessel containing quartz (SiO2) or
alumina (Al2O3). For example, a quartz or alumina vessel can be
used. Of these, if a quartz vessel is used, silicon may intrude into the
alloy and, particularly, intrudes easily into the composite phases, more
particularly the Cu9Zr2 phases. The vessel preferably has a tap
hole in the bottom surface thereof. This allows the melt to be poured
through the tap hole in the subsequent casting step while continuing
injection of an inert gas, thus more readily allowing oxygen to remain in
the alloy. In addition, the melting atmosphere is preferably an inert gas
atmosphere, and particularly, the raw material is preferably melted while
injecting an inert gas so as to apply pressure to the surface of the
alloy. This presumably allows the oxygen contained in the raw material to
remain in the alloy, thus making it more amorphous. The pressure of the
inert gas is preferably 0.5 to 2.0 MPa.

[0077] In the method for producing the copper alloy wire of the present
invention, the inert gas atmosphere is preferably maintained in the
casting step continuously after the melting step so as to apply pressure
to the surface of the alloy. In this case, the inert gas is preferably
injected so as to apply a pressure of 0.5 to 2.0 MPa to the raw material.
In addition, the melt is preferably poured through the tap hole in the
bottom surface of the crucible while injecting the inert gas. This allows
the melt to be poured without contact with outside air (atmospheric air).
In the casting step, the melt is preferably solidified by quenching so
that, according to results of an analysis by the EDX-ZAF method, the
amount of zirconium contained in the copper matrix phases of the ingot at
room temperature after the solidification is supersaturated at 0.3 atomic
percent or more. This is because such solidification by quenching further
increases the ultimate tensile strength. In the copper-zirconium
equilibrium diagram, the solid solubility limit of zirconium is 0.12%.
Although the mold used in the casting step is not particularly limited,
the metal melted in the melting step is preferably poured into a copper
mold or a carbon die because they allow the melt to be more readily
quenched. For production of other-element-free materials, it is
presumably preferable to solidify the melt by quenching so that,
according to results of an analysis by the EDX-ZAF method, the amount of
zirconium is supersaturated at 0.3 atomic percent or more. For production
of other-element-free materials, additionally, the metal melted in the
melting step may be poured into a copper mold or a carbon die.

[0078] In the method for producing the copper alloy wire of the present
invention, the ingot is preferably cold-drawn to a reduction of area of
99.00% or more through one or more drawing passes in the wire drawing.
Preferably, at least one of the drawing passes has a reduction of area of
15% or more. This presumably further increases the ultimate tensile
strength. In the wire drawing step, additionally, the temperature for
cold wire drawing is preferably lower than room temperature (for example,
30° C.), more preferably 25° C. or less, and further
preferably 20° C. or less. This presumably allows deformation
twins to occur more readily, thus further increasing the ultimate tensile
strength. The temperature can be controlled by, for example, cooling at
least one of the material and the equipment for wire drawing (such as a
wire drawing die) to a temperature lower than room temperature before
use. Examples of methods for cooling the material or the equipment
include immersing the material or the equipment in a bath filled with a
liquid and pouring a liquid over the material or the equipment using, for
example, a shower. In this case, the liquid used is preferably cooled in
advance, and it may be cooled, for example, by allowing a coolant to flow
through a cooling pipe provided in the bath filled with the liquid, or by
returning a liquid cooled with a coolant into the bath. For example, the
liquid is preferably a lubricant. This is because, if the material is
cooled with a lubricant, the wire drawing can be more readily performed.
On the other hand, if the equipment is cooled, it may be cooled by
allowing a coolant to flow through, for example, a pipe provided in the
equipment. Examples of coolants for cooling the liquid or the equipment
include hydrofluorocarbons, alcohols, liquid ethylene glycol, and dry
ice. For production of other-element-free materials, presumably such a
wire drawing step may be included.

EXAMPLES

Production of Wire

Example 1

[0079] First, a copper-zirconium binary alloy containing 3.0 atomic
percent of zirconium with the balance being copper was subjected to
levitation melting in an argon gas atmosphere. Next, a pure copper mold
having a round-bar-shaped cavity with a diameter of 3 mm was coated, and
the melt of about 1,200° C. was poured and cast into a round-bar
ingot at about 1,200° C. The diameter of the ingot was determined
to be 3 mm by measurement using a micrometer. FIG. 6 is a photograph of
the round-bar ingot. Next, wire drawing was performed by passing the
round-bar ingot, which had been cooled to room temperature, through 20 to
40 dies having gradually decreasing hole diameters at room temperature so
that the diameter after the wire drawing was 0.300 mm, thus producing a
wire of Example 1. During the process, the drawing speed was 20 m/min.
The diameter of the copper alloy wire was determined to be 0.300 mm by
measurement using a micrometer. FIG. 7 is a photograph of a diamond die
used for drawing. The diamond dies had die holes in the centers thereof,
and the ingot was sequentially passed through the dies of different hole
diameters to perform wire drawing by shearing.

Examples 2 to 4

[0080] A wire of Example 2 was produced in the same manner as in Example 1
except that wire drawing was performed so that the diameter after the
wire drawing was 0.100 mm. In addition, a wire of Example 3 was produced
in the same manner as in Example 1 except that wire drawing was performed
so that the diameter after the wire drawing was 0.040 mm. In addition, a
wire of Example 4 was produced in the same manner as in Example 1 except
that wire drawing was performed so that the diameter after the wire
drawing was 0.010 mm.

Examples 5 to 9

[0081] A wire of Example 5 was produced in the same manner as in Example 1
except that a copper-zirconium binary alloy containing 4.0 atomic percent
of zirconium with the balance being copper was used. In addition, a wire
of Example 6 was produced in the same manner as in Example 5 except that
wire drawing was performed so that the diameter after the wire drawing
was 0.100 mm. In addition, a wire of Example 7 was produced in the same
manner as in Example 5 except that wire drawing was performed so that the
diameter after the wire drawing was 0.040 mm. In addition, a wire of
Example 8 was produced in the same manner as in Example 5 except that
wire drawing was performed so that the diameter after the wire drawing
was 0.010 mm. In addition, a wire of Example 9 was produced in the same
manner as in Example 5 except that wire drawing was performed so that the
diameter after the wire drawing was 0.008 mm.

Examples 10 to 13

[0082] A wire of Example 10 was produced in the same manner as in Example
5 except that a pure copper mold having a diameter of 5 mm was used and
that wire drawing was performed so that the diameter after the wire
drawing was 0.100 mm. In addition, a wire of Example 11 was produced in
the same manner as in Example 10 except that wire drawing was performed
so that the diameter after the wire drawing was 0.040 mm. In addition, a
wire of Example 12 was produced in the same manner as in Example 10
except that wire drawing was performed so that the diameter after the
wire drawing was 0.010 mm. In addition, a wire of Example 13 was produced
in the same manner as in Example 10 except that wire drawing was
performed so that the diameter after the wire drawing was 0.008 mm.

Examples 14 to 16

[0083] A wire of Example 14 was produced in the same manner as in Example
5 except that a pure copper mold having a diameter of 7 mm was used and
that wire drawing was performed so that the diameter after the wire
drawing was 0.100 mm. In addition, a wire of Example 1.5 was produced in
the same manner as in Example 14 except that wire drawing was performed
so that the diameter after the wire drawing was 0.040 mm. In addition, a
wire of Example 16 was produced in the same manner as in Example 14
except that wire drawing was performed so that the diameter after the
wire drawing was 0.010 mm.

Examples 17 to 19

[0084] A wire of Example 17 was produced in the same manner as in Example
5 except that a pure copper mold having a diameter of 10 mm was used and
that wire drawing was performed so that the diameter after the wire
drawing was 0.100 mm. In addition, a wire of Example 18 was produced in
the same manner as in Example 17 except that wire drawing was performed
so that the diameter after the wire drawing was 0.040 mm. In addition, a
wire of Example 19 was produced in the same manner as in Example 17
except that wire drawing was performed so that the diameter after the
wire drawing was 0.010 mm.

Examples 20 to 23

[0085] A wire of Example 20 was produced in the same manner as in Example
1 except that a copper-zirconium binary alloy containing 5.0 atomic
percent of zirconium with the balance being copper was used. In addition,
a wire of Example 21 was produced in the same manner as in Example 20
except that wire drawing was performed so that the diameter after the
wire drawing was 0.100 mm. In addition, a wire of Example 22 was produced
in the same manner as in Example 20 except that wire drawing was
performed so that the diameter after the wire drawing was 0.040 mm. In
addition, a wire of Example 23 was produced in the same manner as in
Example 23 except that wire drawing was performed so that the diameter
after the wire drawing was 0.010 mm.

Examples 24 to 27

[0086] A wire of Example 24 was produced in the same manner as in Example
1 except that a copper-zirconium binary alloy containing 6.8 atomic
percent of zirconium with the balance being copper was used. In addition,
a wire of Example 25 was produced in the same manner as in Example 24
except that wire drawing was performed so that the diameter after the
wire drawing was 0.100 mm. In addition, a wire of Example 26 was produced
in the same manner as in Example 24 except that wire drawing was
performed so that the diameter after the wire drawing was 0.040 mm. In
addition, a wire of Example 27 was produced in the same manner as in
Example 24 except that wire drawing was performed so that the diameter
after the wire drawing was 0.010 mm.

Comparative Example 1

[0087] A wire of Comparative Example 1 was produced in the same manner as
in Example 1 except that a copper-zirconium binary alloy containing 2.5
atomic percent of zirconium with the balance being copper was used, and
that wire drawing was performed so that the diameter after the wire
drawing was 0.100 mm.

Comparative Example 2

[0088] In Comparative Example 2, wire drawing was performed in the same
manner as in Example 1 except that a copper-zirconium binary alloy
containing 7.4 atomic percent of zirconium with the balance being copper
was used and that wire drawing was performed so that the diameter after
the wire drawing was 0.100 mm, although the wire was broken during the
wire drawing.

Comparative Example 3

[0089] A copper-zirconium binary alloy containing 8.7 atomic percent of
zirconium with the balance being copper was subjected to levitation
melting and was cast into a round-bar ingot by pouring it into a pure
copper mold having a diameter of 7 mm, although the ingot was cracked
during the casting and could not be subjected to the subsequent wire
drawing step.

Comparative Example 4

[0090] A wire of Comparative Example 4 was produced in the same manner as
in Example 5 except that a pure copper mold having a diameter of 12 mm
was used and that wire drawing was performed so that the diameter after
the wire drawing was 0.600 mm.

Comparative Example 5

[0091] A wire of Comparative Example 5 was produced in the same manner as
in Example 5 except that a pure copper mold having a diameter of 7 mm was
used and that wire drawing was performed so that the diameter after the
wire drawing was 0.800 mm.

[0092] Observation of Casting Structure

[0093] The ingots before the wire drawing were cut in a circular
cross-section perpendicular to the axial direction, were mirror-polished,
and were observed by SEM (SU-70, manufactured by Hitachi, Ltd.). FIG. 8
is an SEM photograph of the casting structure of an ingot containing 4.0
atomic percent of zirconium and having a diameter of 5 mm. The white
regions are eutectic phases of copper and Cu9Zr2, and the black
regions are proeutectic copper matrix phases. The secondary DAS was
measured using the SEM photographs. Table 1 shows the values of the
secondary DAS of Examples 1 to 27 and Comparative Examples 1 to 5. Table
1 shows the secondary DAS, the alloy composition, casting diameter, and
drawing diameter described above, and the reduction of area, eutectic
phase fraction, phase pitch, amorphous fraction, ultimate tensile
strength, and electrical conductivity described below.

[0095] First, the cross-sectional area of each ingot before the wire
drawing was determined from the diameter thereof, and the cross-sectional
area after the wire drawing was determined from the diameter of the
copper alloy wire. From these values, the cross-sectional areas before
and after the wire drawing and the reduction of area were determined. The
reduction of area (%) is the value represented by {(cross-sectional area
before wire drawing-cross-sectional area after wire
drawing)×100}/(cross-sectional area before wire drawing).

[0096] Observation of Structure after Wire Drawing

[0097] The copper alloy wires after the wire drawing were cut in a
circular cross-section perpendicular to the axial direction, were
mirror-polished, and were observed by SEM. FIG. 9 is a set of SEM
photographs of the copper alloy wire of Example 6 in a circular
cross-section perpendicular to the axial direction. FIG. 9(b) is a
magnified view of the region enclosed by the rectangle in the center of
FIG. 9(a). The white regions are eutectic phases, and the black regions
are copper matrix phases. The black-and-white contrast of the SEM
photograph was divided into the copper matrix phases and the eutectic
phases by binarization, and the area fraction of the eutectic phases was
determined as the eutectic phase fraction. FIG. 10 is a set of SEM
photographs of the copper alloy wire of Example 6 in a cross-section
parallel to the axial direction and including the central axis. FIG.
10(b) is a magnified view of the region enclosed by the rectangle in the
center of FIG. 10(a). The white regions are eutectic phases, and the
black regions are copper matrix phases; they were arranged in a staggered
manner to form a fibrous structure extending in one direction. In this
regard, an analysis of the field of view in FIG. 10 by energy dispersive
X-ray spectroscopy (EDX) revealed that the black regions were matrix
phases formed only of copper and the white regions were eutectic phases
containing copper and zirconium. Next, the phase pitch of copper and
Cu9Zr2 was measured by STEM as follows. First, a wire thinned
by argon ion milling was prepared as a sample for STEM observation. Then,
the central region, serving as a representative region, was observed at a
magnification of 500,000 times, and scanning electron microscopy
high-angle annular dark-field images (STEM-HAADF images) were acquired in
three fields of view of 300 nm×300 nm. The widths of the phases in
the STEM-HAADF images were measured, and the average thereof was
calculated as the measured phase pitch. FIG. 11 is an STEM photograph,
taken by STEM (JEM-2300F, manufactured by JEOL Ltd.), of a white region
(eutectic phase) in FIG. 9. An EDX analysis indicated that the white
regions were copper and the black regions were Cu9Zr2. In
addition, the presence of Cu9Zr2 was confirmed by analyzing a
diffraction image by selected-area diffraction and measuring the lattice
parameters of a plurality of diffraction planes. Thus, it was
demonstrated that the eutectic phase in FIG. 11 had a double fibrous
structure in which copper and Cu9Zr2 were arranged alternately
at a substantially regular pitch, namely, about 20 nm. The phase pitch is
the pitch of the alternately arranged copper and Cu9Zr2
measured by STEM observation of the eutectic phases. When the lattice
image of the eutectic phase shown in FIG. 11 was observed by STEM at a
magnification of 2,500,000 times in a field of view of 50 nm×50 nm,
about 15% of amorphous phases were recognized in terms of area fraction
in the field of view (eutectic phase). FIG. 12 schematically shows the
amorphous phases in the eutectic phase. The amorphous phases were mainly
formed at the interfaces between the copper matrix phases and the
Cu9Zr2 compound phases, presumably contributing to maintaining
sufficient mechanical strength. The amorphous fraction was determined by
measuring the area fraction of possible amorphous regions where atoms
were randomly arranged in the lattice image. In addition, when, the
copper structure in FIG. 11, which looks white, was observed by STEM, the
difference in orientation between the adjacent fine crystals was
extremely small, namely, about 1° to 2°. This suggests that
large shear slip deformation occurred in copper in the drawing direction
without aggregation of dislocations. This presumably allows wire drawing
at high drawing ratio without causing a break during the cold working.

[0098] Measurement of Ultimate Tensile Strength

[0099] The ultimate tensile strength was measured according to JIS Z2201
using a universal testing machine (Autograph AG-1kN, manufactured by
Shimadzu Corporation). The ultimate tensile strength of each copper alloy
wire was determined by dividing the maximum load by the initial
cross-sectional area.

[0100] Measurement of Electrical Conductivity

[0101] The electrical conductivity of each wire was determined by
measuring the electrical resistivity (volume resistivity) of the wire at
room temperature according to JIS H0505 using a four-electrode electrical
resistivity meter, calculating the ratio of the measured electrical
resistivity to the resistivity (1.7241 μΩcm) of annealed pure
copper (standard soft copper having an electrical resistivity of 1.7241
μΩcm at 20° C.), and converting it to electrical
conductivity (% IACS: International Annealed Copper Standard). The
conversion was performed by the following equation: electrical
conductivity γ (% IACS)=1.7241/volume resistivity ρ×100.

[0102] Experimental Results

[0103] As shown in Table 1, when the zirconium content fell below 3.0
atomic percent, the ultimate tensile strength was decreased (Comparative
Example 1). The reason is presumably that an amount of eutectic phases
large enough to ensure sufficient strength was not formed because the
zirconium content was low. On the other hand, when the zirconium content
exceeded 7.0 atomic percent, no desired wire could be obtained because a
break occurred during the wire drawing (Comparative Example 2) or a crack
occurred during the casting (Comparative Example 3). In addition, even
though the zirconium content fell within the range of 3.0 to 7.0 atomic
percent, the ultimate tensile strength was decreased when the secondary
DAS of the casting structure was excessive (Comparative Example 4) or the
reduction of area fell below 99.00% (Comparative Example 5). This is
presumably because an amount of eutectic phases large enough to ensure
sufficient strength was not formed. In contrast, Examples 1 to 27
achieved an ultimate tensile strength exceeding 1,300 MPa and an
electrical conductivity exceeding 20% IACS without suffering a casting
crack or a break during the production. Thus, it was demonstrated that
the production method of the present invention provides a desired copper
alloy wire by cold working without heat treatment. In addition, it was
demonstrated that the casting diameter, the secondary DAS, and the
reduction of area can be appropriately controlled for a particular
composition to achieve the desired eutectic phase fraction, the desired
phase pitch of copper and Cu9Zr2 in the eutectic phases, and
the desired amorphous fraction, thus achieving an ultimate tensile
strength exceeding 1,300, 1,500, or 1,700 MPa and an electrical
conductivity exceeding 20% IACS. In particular, it was demonstrated that
the ultimate tensile strength becomes higher with increasing zirconium
content, increasing eutectic phase fraction, and increasing amorphous
fraction. Hence, presumably the copper matrix phases contribute to
electrical conductivity as a path for free electrons, whereas the
eutectic phases contribute to ultimate tensile strength. In the eutectic
phases, additionally, presumably copper contributes to electrical
conductivity, whereas the eutectic phases contribute to ultimate tensile
strength. It was also demonstrated that a high-strength copper alloy wire
having such wire properties can be achieved as-drawn with a diameter of
0.100, 0.040, or 0.010 mm or less.

[0104] In the above experiment, the properties of other-element-free
materials produced so as to contain as small amounts of elements other
than copper and zirconium as possible were examined. To examine the
properties of other-element-containing materials produced so as to
contain elements other than copper and zirconium, the following
experiment was further carried out.

Example 28

[0105] First, an alloy containing 3.0 atomic percent of zirconium and 700
to 2,000 ppm by mass of oxygen with the balance being copper was put into
a quartz nozzle having a tap hole in the bottom surface thereof, and
after the nozzle was evacuated to 5×10-2 Pa and was then
purged with argon gas to nearly the atmospheric pressure, the alloy was
melted into liquid metal in an arc melting furnace while applying a
pressure of 0.5 MPa to the liquid surface. Next, a pure copper mold
having a round-bar-shaped cavity with a diameter of 3 mm and a length of
60 mm was coated, and the melt of about 1,200° C. was poured and
cast into a round-bar ingot. The melt was poured by opening the tap hole
formed in the bottom surface of the quartz nozzle while applying pressure
with argon gas. Next, the round-bar ingot, which had been cooled to room
temperature, was subjected to cold drawing to a diameter of 0.5 mm using
a cemented carbide die at room temperature and was then subjected to
continuous cold wire drawing to a diameter of 0.160 mm using diamond
dies, thus producing a wire of Example 28. The continuous wire drawing
was performed with the wire and the diamond dies immersed in a bath
filled with an aqueous liquid lubricant. During this process, the liquid
lubricant in the bath was cooled with a cooling pipe using liquid
ethylene glycol as a coolant. The reduction of area at which the 3 mm
round-bar ingot was drawn to a diameter of 0.5 mm was 97.2%, and the
reduction of area at which the 3 mm round-bar ingot was drawn to a
diameter of 0.160 mm was 99.7%.

Example 29

[0106] A wire of Example 29 was produced in the same manner as in Example
28 except that wire drawing was performed so that the diameter after the
wire drawing was 0.040 mm.

Examples 30 to 34

[0107] A wire of Example 30 was produced in the same manner as in Example
28 except that an alloy containing 4.0 atomic percent of zirconium and
700 to 2,000 ppm by mass of oxygen with the balance being copper was used
and that wire drawing was performed so that the diameter after the wire
drawing was 0.200 mm. In addition, a wire of Example 31 was produced in
the same manner as in Example 30 except that wire drawing was performed
so that the diameter after the wire drawing was 0.160 mm. In addition, a
wire of Example 32 was produced in the same manner as in Example 30
except that wire drawing was performed so that the diameter after the
wire drawing was 0.070 mm. In addition, a wire of Example 33 was produced
in the same manner as in Example 30 except that wire drawing was
performed so that the diameter after the wire drawing was 0.040 mm. In
addition, a wire of Example 34 was produced in the same manner as in
Example 30 except that wire drawing was performed so that the diameter
after the wire drawing was 0.027 mm.

Examples 35 to 36

[0108] A wire of Example 35 was produced in the same manner as in Example
28 except that an alloy containing 5.0 atomic percent of zirconium and
700 to 2,000 ppm by mass of oxygen with the balance being copper was used
and that wire drawing was performed so that the diameter after the wire
drawing was 0.160 mm. In addition, a wire of Example 36 was produced in
the same manner as in Example 35 except that wire drawing was performed
so that the diameter after the wire drawing was 0.040 mm.

Comparative Example 6

[0109] A wire of Comparative Example 6 was produced in the same manner as
in Example 30 except that wire drawing was performed so that the diameter
after the wire drawing was 0.500 mm.

[0110] Derivation of Drawing Ratio

[0111] First, the cross-sectional area A0 of each ingot before the
wire drawing was determined from the diameter thereof, and the
cross-sectional area A1 after the wire drawing was determined from
the diameter of the copper alloy wire. From these values, the drawing
ratio η represented by the equation η=ln(A0/A1) was
determined.

[0112] Observation of Casting Structure

[0113] The ingots before the wire drawing were cut in a circular
cross-section perpendicular to the axial direction (hereinafter also
referred to as "lateral cross-section"), were mirror-polished, and were
observed by optical microscopy. FIG. 13 is a set of optical micrographs
of the casting structures of the ingots containing 3.0 to 5.0 atomic
percent of zirconium. FIG. 13(a) shows the casting structures of the
ingots of Examples 28 and 29 containing 3.0 atomic percent of zirconium,
FIG. 13(b) shows the casting structures of the ingots of Examples 30 to
34 containing 4.0 atomic percent of zirconium, and FIG. 13(c) shows the
casting structures of the ingots of Examples 35 and 36 containing 5.0
atomic percent of zirconium. The bright regions are proeutectic
α-copper phases (copper matrix phases), and the dark regions are
eutectic phases (composite phases). FIG. 13 demonstrates that the amount
of eutectic phases increases with increasing zirconium content. The
secondary DAS was measured using the optical micrographs. In FIG. 13(a),
the secondary DAS was 2.7 μm. In FIGS. 13(b) and 13(c), however, the
secondary DAS could not be determined because the dendrite arms became
nonuniform as the amount of α-copper phases decreased with
increasing zirconium content.

[0114] In addition, the ingots before the wire drawing were cut in a
circular cross-section perpendicular to the axial direction, were
mirror-polished, and were observed by SEM. FIG. 14 is an SEM photograph
(composition image) of the casting structures of the ingots of Examples
28 and 29 containing 3.0 atomic percent of zirconium. According to an EDX
analysis of the bright and dark regions in the structure, the bright
regions contained 93.1 atomic percent of copper and 6.9 atomic percent of
zirconium, and the dark regions contained 99.7 atomic percent of copper
and 0.3 atomic percent of zirconium. This demonstrates that the bright
regions were eutectic phases (composite phases) and the dark regions were
α-copper phases (copper matrix phases). Because the solid
solubility limit of zirconium in the copper phases is 0.12 atomic percent
in the equilibrium diagram of copper-zirconium alloy, the fact that 0.3
atomic percent of zirconium was dissolved in the copper phases of the
ingots of the copper alloys containing 3 atomic percent of zirconium
suggests that the solid solubility limit of zirconium in the copper
phases was extended as a result of solidification by quenching.

[0115] Observation of Structure after Wire Drawing

[0116] The copper alloy wires after the wire drawing were cut in a
circular cross-section perpendicular to the axial direction (hereinafter
referred to as "lateral cross-section") and a cross-section parallel to
the axial direction and including the central axis (hereinafter also
referred to as "longitudinal cross-section"), were mirror-polished, and
were observed by SEM. FIG. 15 is a set of SEM photographs (composition
images) of the cross-sections of the copper alloy wire of Example 28
(copper alloy containing 3 atomic percent of zirconium; η=5.9). The
lateral cross-section was nearly a perfect circle, and no damage, such as
a crack, other than scratches formed during the working was observed in
the side surface. This demonstrates that high-strain wire drawing can be
performed without heat treatment. FIG. 16 is a set of SEM photographs of
the surface of the copper alloy wire of Example 36 (copper alloy
containing 5 atomic percent of zirconium; η=8.6). The surface of the
wire was smooth only with some scratches, demonstrating that continuous
cold wire drawing can be performed without annealing. In addition, for
example, as shown in Table 2, it was demonstrated that wire drawing
without heat treatment can be performed at least at a drawing ratio η
of 8.6 to a minimum diameter of 40 μm. Furthermore, it was
demonstrated that wire drawing without heat treatment can be performed at
least at a drawing ratio η of 9.4 to a minimum diameter of 27 μm.
As observed in the longitudinal cross-section shown in FIG. 15(a), the
α-copper phases and the eutectic phases were arranged in a
staggered manner to form a fibrous structure extending in one direction.
As observed in the lateral cross-section in. FIG. 15(b), additionally,
the casting structure of the α-copper phases and the eutectic
phases of the ingot was broken. In addition, fine particles dispersed in
a black spot pattern were observed in the α-copper phases. An EDX
analysis of these particles detected oxygen in an amount 4.7 times the
amount of oxygen in the eutectic phases as well as copper and zirconium,
suggesting the presence of oxide. The bright regions (eutectic phases)
and the dark regions (α-copper phases) in the structure in the
lateral cross-section in FIG. 15(b) were binarized, and the area fraction
of the eutectic phases was determined to be 43%. Among the examples where
n=5.9, the area fraction of the eutectic phases was 49% in Example 31
(copper alloy containing 4 atomic percent of zirconium) and was 55% in
Example 35 (copper alloy containing 5 atomic percent of zirconium). This
demonstrates that the area fraction of the eutectic phases increases with
the zirconium content.

[0117] FIG. 17 is a set of STEM photographs of a eutectic phase in the
copper alloy wire of Example 31 (copper alloy containing 4 atomic percent
of zirconium; η=5.9). FIG. 17(a) shows a bright-field (BF) image,
FIG. 17(b) shows a high-angle annular dark-field (HAADF) image, FIG.
17(c) shows an elemental map of Cu--Kα, FIG. 17(d) shows an
elemental map of Zr-Lα, FIG. 17(e) shows the results of an
elemental analysis at point A in the bright regions in FIG. 17(b), and
FIG. 17(f) shows the results of an elemental analysis at point B in the
dark regions in FIG. 17(b). The arrow in the BF image indicates the
orientation of the drawing axis (DA). In the HAADF image, the bright
regions and the dark regions formed a layered structure and were arranged
at a pitch of about 20 nm. It was demonstrated that the bright regions
were α-copper phases and the dark regions were compound phases
containing copper and zirconium. The ratio of the α-copper phases
to the compound phases containing copper and zirconium observed in the
image was measured to be about 60:40 to 50:50, suggesting that the rule
of mixture also applies to the interiors of the eutectic phases. FIG. 18
is a set of STEM photographs of a eutectic phase in the copper alloy wire
of Example 31 (copper alloy containing 4 atomic percent of zirconium;
η=5.9). FIG. 18(a) shows an STEM-BF image, and FIG. 18(b) shows a
selected-area electron beam diffraction (SAD) image taken from the circle
shown in FIG. 18(a). In the SAD image in FIG. 18(b), ring patterns were
observed aside from diffraction spots, which indicate the copper phases.
The lattice parameters of the three diffraction rings shown in FIG. 18(b)
were determined to be d1=0.2427 nm, d2=0.1493 nm, and
d3=0.1255 nm, respectively. On the other hand, Table 3 compares the
lattice parameters of the (202), (421), and (215) planes of
Cu9Zr2 determined by Glimois et al. The lattice parameters
shown above can be assumed to be equivalent to those in Table 3 within
the limits of error, suggesting that the compound observed in FIG. 18(a)
that contained copper and zirconium was Cu9Zr2.

[0119] FIG. 19 is a set of graphs showing the relationships between the
area fraction of eutectic phases (eutectic phase fraction) and the
electrical conductivity (EC), ultimate tensile strength (UTS), and 0.2%
offset yield strength (σ0.2) of the examples where the drawing
ratio η was 5.9, namely, Example 28 (copper alloy containing 3 atomic
percent of zirconium), Example 31 (copper alloy containing 4 atomic
percent of zirconium), and Example 35 (copper alloy containing 5 atomic
percent of zirconium). The EC decreased with increasing area fraction of
the eutectic phases. Conversely, the UTS and the σ0.2 both
increased with increasing area fraction of the eutectic phases. The
decrease in EC is presumably related to the fact that the amount of
α-copper phases decreased relatively as the area fraction of the
eutectic phases increased, whereas the increases in UTS and
σ0.2 are presumably related to the fact that the amount of
Cu9Zr2 compound phases in the eutectic phases increased
relatively as the area fraction of the eutectic phases increased.

[0120] FIG. 20 is a set of graphs showing the relationships between the
drawing ratio η and the EC, UTS, and σ0.2 of Examples 30
to 34, which are copper alloy wires containing 4.0 atomic percent of
zirconium. The EC of the ingots, that is, as-cast, was 28% IACS; the EC
of the copper alloy wires after the wire drawing was higher than that of
the ingots and was maximized around η=3.6, but decreased at higher
drawing ratios. The UTS and the σ0.2, on the other hand,
increased linearly with increasing drawing ratio.

[0121] FIG. 21 is a set of SEM photographs of longitudinal cross-sections
of the copper alloy wires containing 4.0 atomic percent of zirconium,
where FIG. 21(a) shows Example 31 (η=5.9), FIG. 21(b) shows Example
32 (η=7.5), and FIG. 21(c) shows Example 33 (η=8.6). It was
demonstrated that the layered structure of the α-copper phases and
the eutectic phases changes to a denser structure including thinner
layers with increasing drawing ratio. This change of the layered
structure is presumably related to the relationships between the drawing
ratio η and the EC, UTS, and σ0.2 shown in FIG. 20.
Furthermore, presumably the layered structure of the copper phases and
the Cu9Zr2 compound phases formed in the eutectic phases
changes with the drawing ratio η and affects the electrical and
mechanical properties.

[0122] FIG. 22 is a graph showing the relationships between the annealing
temperature and the EC and UTS of annealed samples of the copper alloy
wire of Example 28 (copper alloy containing 3 atomic percent of
zirconium; η=5.9). The annealing was performed by maintaining the
samples at various temperatures within the range of 300° C. to
650° C. for 900 seconds and then cooling them in the furnace. The
EC remained nearly the same within the range of room temperature to
300° C., but increased gradually at higher temperatures. The UTS
was maximized at 350° C., decreased gradually, and decreased
abruptly above 475° C. One possible cause for this is
precipitation of zirconium dissolved in the α-copper phases. The
electrical and mechanical properties of the drawn wire, which are
presumably affected by the structure, were relatively stable up to
475° C., whereas the structure presumably changed at higher
temperatures. This suggests that the copper alloy wire of the present
invention can be stably used up to 475° C.

[0123] FIG. 23 is a graph showing the nominal S-S curve of the copper
alloy wire of Example 36 (copper alloy containing 5 atomic percent of
zirconium; η=8.6). The ultimate tensile strength was 2,234 MPa, the
0.2% offset yield strength was 1,873 MPa, the Young's modulus was 126
GPa, and the elongation was 0.8%. In addition, the electrical
conductivity was 16% IACS. This demonstrates that it is possible to
achieve an ultimate tensile strength of 2,200 MPa or more, an electrical
conductivity of 15% AICS or more, and a Young's modulus of 110 to 140 GPa
or more. In addition, whereas the ultimate tensile strength exceeded 2
GPa, the Young's modulus was about half that of a practical copper alloy,
demonstrating that the break elongation is generally high.

[0124] FIG. 24 is an SEM photograph of the fracture surface of the copper
alloy wire of Example 36 (copper alloy containing 5 atomic percent of
zirconium; η=8.6) after the tensile test. A vein pattern was
partially observed, indicating the fracture properties of amorphous
alloys.

[0125] FIG. 25 is a set of STEM photographs of a composite phase in a
longitudinal cross-section of the copper alloy wire of Example 33 (copper
alloy containing 4 atomic percent of zirconium; η=8.6). FIG. 25(a)
shows a BF image, and FIG. 25(b) shows an HAADF image. In FIG. 25,
layered copper phases having a width of about 10 to 70 nm and
Cu9Zr2 phases extending from the ends thereof in a stringer
pattern were observed. The Cu9Zr2 phases extending in a
stringer pattern had an average width of not more than 10 nm,
demonstrating that they become thinner (finer) with increasing drawing
ratio. Thus, presumably the ultimate tensile strength can be increased,
for example, as the copper-zirconium compound phases, such as the
Cu9Zr2 phases, become finer, and particularly, can be further
increased if the average width is 10 nm or less. The copper phases, which
are easy to recognize in the BF image in FIG. 25(a), are layered regions.
The Cu9Zr2 phases, which are easy to recognize in the HADDF
image in FIG. 25(b), are black regions extending in a stringer pattern.
In addition, as observed in the BF image in FIG. 25(a), deformation twins
also appeared in the copper phases at an angle of about 20° to
40° with respect to the drawing axis.

[0126] Table 4 shows the results of a quantitative analysis by the ZAF
method on the Cu9Zr2 phases and the copper phases in the
composite phases and the copper matrix phases (α-copper phases) of
the copper alloy wire of Example 33 (copper alloy containing 4 atomic
percent of zirconium; η=8.6). According to Table 4, the
Cu9Zr2 contained oxygen. This oxygen presumably increased the
ultimate tensile strength by making the copper alloy more amorphous. On
the other hand, no oxygen was contained in the copper matrix phases or
the copper phases in the composite phases. In addition, silicon was
contained in both the Cu9Zr2 phases and the copper phases in
the composite phases. This silicon was presumably derived from the quartz
nozzle. Rather than silicon, presumably aluminum may be contained. For
example, presumably aluminum is contained if, for example, an alumina
nozzle is used.

[0127] FIG. 26 shows the results of an EDX analysis of a eutectic phase
(points 1 to 4) in the copper alloy wire of Example 33 (copper alloy
containing 4 atomic percent of zirconium; η=8.6). In addition, FIG.
27 shows the results of an EDX analysis of a copper matrix phase (points
5 and 6) in the copper alloy wire of Example 33. Points 1 to 6 correspond
to points 1 to 6, respectively, shown in Table 4. The photograph shown in
FIG. 26 is an STEM-HAADF image that is a magnified photograph of the
enclosed region in FIG. 25, and points A and B in the STEM-HAADF image
correspond to points 3 and 4, respectively. At the points in the
Cu9Zr2 phases, which look dark in the STEM-HAADF image, large
amounts of oxygen and silicon were contained, and the mean atomic number
Z calculated from the oxygen, silicon, copper, and zirconium
concentrations quantified by the ZAF method was 20.2, demonstrating that
the mean atomic number Z was apparently lower than that of copper,
namely, 29. This is presumably the reason why the Cu9Zr2 phases
look darker than the copper phases. The STEM-HAADF image of the field of
view in which the EDX analysis was performed at points 1 and 2 is not
shown. On the other hand, the photograph shown in FIG. 27 is an STEM-BF
image of a copper matrix phase (α-copper phase), and points 5 and 6
in the STEM-BF image correspond to points 5 and 6, respectively. In the
STEM-BF image, a layered structure was found in the α-copper phase,
and deformation twins were partially observed therein. The average width
of the individual layers, that is, copper phases, in the layered
structure was not more than 100 nm. Thus, if a layered structure is
formed in the α-copper phases, presumably the ultimate tensile
strength can be increased by the effect similar to the Hall-Petch law,
and can be further increased if the average width of the copper phases is
100 nm or less. In addition, the deformation twins were formed so as not
to straddle the boundaries between the copper phases. These deformation
twins were oriented at an angle of 20° to 40° with
reference to the axial direction and occupied 0.1% to 5% of the copper
matrix phase. If such deformation twins are contained, presumably the
ultimate tensile strength can be increased as a result of twinning
without significantly decreasing the electrical conductivity. It was
confirmed that they were not traces of ion milling. In addition, it was
demonstrated that the copper matrix phases contained no oxygen or
silicon, or only trace amounts of oxygen and silicon that could not be
quantified by the ZAF method. In addition, no sign of formation of
dislocation substructures, where the dislocation density is clearly high,
was recognized in the α-copper phases or the copper-zirconium
compound phases, demonstrating that almost no dislocations were present
at least in a longitudinal cross-section. In general, dislocations tend
to increase with increasing drawing ratio; in the case of the present
application, presumably dislocations increased negligibly because they
were absorbed into, for example, the boundaries between the phases or the
deformation twins, or disappeared. Accordingly, good electrical
conductivity was achieved presumably because almost no dislocations were
present in the axial direction. This also applied to other examples, such
as those where the zirconium content was 5 atomic percent.

[0128] FIG. 28 is a set of STEM-BF images of the copper alloy wire of
Example 33 (copper alloy containing 4 atomic percent of zirconium;
η=8.6), showing the results of observations of the enclosed regions
in the STEM-HAADF image in FIG. 26. FIG. 28(a) shows an STEM-BF image of
the larger frame in FIG. 26, and FIG. 28(b) shows an STEM-BF image of the
smaller frame in FIG. 26. Although the copper phases were shaded at some
observation sites, lattice fringes were observed. In the Cu9Zr2
phase enclosed by the solid lines, on the other hand, no lattice fringe
was observed, demonstrating that the Cu9Zr2 phase was
amorphous. In FIG. 28, the area fraction of the amorphous phase was
determined to be about 31%. This demonstrates that amorphous phases tend
to be formed in copper-zirconium compound phases such as Cu9Zr2
phases. In this regard, presumably the Cu9Zr2 phases may be
amorphous phases in the entirety thereof, rather than in part.

[0129] FIG. 29 is a set of graphs showing the relationships between the
eutectic phase fraction measured in a lateral cross-section at a drawing
ratio η of 5.9 (intermediate diameter: 160 μm) and the UTS,
σ0.2, Young's modulus, EC, and elongation of the copper alloy
wires of the examples where the drawing ratio η was 8.6, namely,
Example 29 (copper alloy containing 3 atomic percent of zirconium),
Example 33 (copper alloy containing 4 atomic percent of zirconium), and
Example 36 (copper alloy containing 5 atomic percent of zirconium). It
was demonstrated that the UTS and the σ0.2 increase with
increasing eutectic phase fraction. It was also demonstrated that the
Young's modulus decreases with increasing eutectic phase fraction. It was
also demonstrated that the EC and the elongation are maximized when the
eutectic phase fraction is about 50%. The individual properties are
presumably related to the presence of the Cu9Zr2 compound
phases and the structural change (becoming more amorphous) in the
eutectic phases.

[0130] FIG. 30 is a set of graphs showing the relationships between the
drawing ratio and the UTS, σ0.2, structure, and EC of the
copper alloy wires containing 4 atomic percent of zirconium, namely,
Examples 30 to 34. It was demonstrated that the strength and the Young's
modulus increase with increasing drawing ratio. In addition, a comparison
between the examples where η=5.9 and the examples where η=8.6
demonstrates that the average widths of the α-copper phases and the
Cu9Zr2 compound phases decrease with increasing drawing ratio.

[0131] FIG. 31 summarizes the results of the examinations of the
relationships between the zirconium content and drawing ratio η and
the changes in layered structure and properties. It was demonstrated that
a copper alloy wire drawn at a higher drawing ratio, such as one drawn at
a drawing ratio η of 8.6, has a higher ultimate tensile strength. In
addition to the improvement in ultimate tensile strength based on the
rule of mixture, the following reasons are presumed. For example,
presumably the ultimate tensile strength can be increased by the effect
similar to the Hall-Petch law because the copper matrix phases are
further layered, and can be increased because deformation twins occur in
the copper matrix phases. In addition, presumably the ultimate tensile
strength can be increased with increasing drawing ratio because, for
example, the Cu9Zr2 compound phases become thinner and more
dispersed (stringer dispersion). In addition, the alloy becomes more
amorphous with increasing drawing ratio; presumably it enhances the
effect of making the alloy more amorphous by the possible presence of
oxygen. In addition, presumably the Young's modulus tends to decrease
because the alloy tends to become more amorphous as the Cu9Zr2
phases increase with increasing zirconium content.

[0132] Table 5 shows the experimental results of Examples 28 to 36 and
Comparative Example 6. Table 5 lists the secondary DAS, the alloy
composition, the casting diameter, the drawing diameter, the reduction of
area, the drawing ratio, the ultimate tensile strength, and the
electrical conductivity. In addition, FIG. 32 is a graph showing the
relationships between the UTS and EC of the copper alloy wires of
Examples 28 to 36 and Comparative Example 6, together with those of
typical known copper alloys for comparison. The results of the copper
alloy wires of Examples 28 to 36 and Comparative Example 6 are shown
along the solid line. On the other hand, the results of the typical known
copper alloys are shown along the broken lines. In general, it is well
known that there is a trade-off relationship between UTS and EC: as
indicated by the broke lines, the EC decreases shapely with increasing
UTS. It was demonstrated, however, that the relationship was gentler for
the copper alloy wires of hypoeutectic compositions of Examples 28 to 36
of the present application and Comparative Example 6, as indicated by the
solid line, than for the typical known copper alloys. This is because the
layered structure could change continuously in association with the
drawing ratio (η) during the wire drawing process, presumably
contributing to alleviation of the trade-off relationship between UTS and
EC. Whereas a quartz nozzle was used to dissolve the raw material in
Examples 28 to 36, presumably the vessel used is not limited thereto and
may be a vessel containing quartz. In addition, presumably a vessel
containing aluminum may be used. In addition, whereas the molten metal
was poured into a copper mold in Examples 1 to 36, presumably it may be
directly poured into, for example, a carbon die.

[0133] The present application claims priorities from the Japanese Patent
Application No. 2009-212053 filed on Sep. 14, 2009, and the U.S.
Provisional Application No. 61/372,185 filed on Aug. 10, 2010, the entire
contents of both of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

[0134] The present invention is applicable in the field of wrought copper
products.